This invention relates to the manufacture of devices that include a ceramic layer, and, more particularly, to a reliable, inexpensive approach for preparing such a device with a very thin ceramic layer.
Ceramics are used in a wide variety of devices because of their unique properties. For example, many ceramics have low electrical conductivity and are therefore useful as dielectric insulators in devices such as capacitors and microelectronic devices. Other ceramics having high ionic conductivity can act as solid electrolytes in applications such as fuel cells and electrochemical storage cells.
In such devices, the ceramic is generally present as a thin layer between or adjacent to electrical conductors or electrodes. The operating principles of such devices, as well as the general need in many devices to improve performance and reduce weight and space requirements, dictate that the ceramic layer should be made as thin as possible consistent with other physical requirements such as sufficient strength and an absence of defects such as pinholes through the ceramic layer.
There are two types of approaches for preparing thin ceramic layers for use in such devices, powder-based techniques and direct deposition techniques. In the powder-based approach, the ceramic is furnished as a powder which is suspended in a fluid or mixed with a binder and a plasticizer. The fluid or binder/plasticizer aid in the handling and forming of the ceramic particles. The flowable mixture is formed into the required shape, the fluid or binder/plasticizer is removed by heating, and the solid ceramic is sintered to its final density. At present, the powder-based techniques of this type have been used to produce layers of about 25 micrometers (0.001 inch) or more in thickness.
In the direct deposition approach, a layer of ceramic is deposited from a bulk or gaseous source onto a substrate by a transport process such as physical vapor deposition or chemical vapor deposition. These direct deposition techniques can produce arbitrarily thin ceramic layers, down to the atomic thickness range in some cases. However, they are usually slow and difficult to implement in many production operations because they require complex deposition apparatus and often require line-of-sight to the deposition region from the source of the ceramic. These techniques may also be limited as to the compositions and degrees of porosity that can be prepared.
A number of devices such as capacitors, solid oxide fuel cells, and solid electrolyte electrochemical storage cells are commonly manufactured using ceramic layers made by conventional powder-based techniques. In general, currently the thickness of the ceramic layers made by those techniques is about 25 micrometers. Direct deposition techniques are also used in some cases, but they are too slow and costly for most applications. Such devices would benefit from the ability to economically manufacture them with thinner ceramic layers, on the order of 10 micrometers in thickness or less. There is therefore a need for an improved approach by which devices having thin ceramic layers can be fabricated.